First, set up an equation to model the number of employees.
y = mx + b, where m = slope and b = y-int
y = 6n + 72
This means that, for every month, n, 6 more employees will be added to the 72 that the company began with.
To find out how many months it will take to double the amount of employees, use the following equation:
(72 x 2) = 6n + 72
144 = 6n + 72
144 - 72 = 6n
72 = 6n
72 / 6 = n
12 = n
It will take 12 months for the number of employees to double.